meh the emperor's character is inconsistent. He couldn't give a shit about his kids and he didn't even know the princess' name yet he got angry because someone was attacking her? Now, one might argue that he wasn't angry for her sake but because his authority was being questioned by someone planning an assassination under his nose.
But that can't be it either since it's a known fact that concubines plot against each other and kill each others' children to increase their own son's chance of getting the throne so by not assigning them any protection and by ignoring the kids, it was obvious he was sentencing them to death. Again, one might argue "hey he might've ignored them for their own sake so that they wouldn't be targetted like children who are favored by the emperor" but that can't be it either since he didn't even know his daughter's name (unless that's some A+ acting there)